The comet assay as a tool in human biomonitoring exposure to volatile organic compounds - a systematic review and meta-analysis.

Exposure to volatile organic compounds (VOCs) such as benzene, styrene, toluene and formaldehyde is associated with genotoxicity and increased risk of cancer. In this systematic review and meta-analysis, we have assessed the effects of VOCs exposure on levels of DNA strand breaks in leukocytes, measured by the comet assay, in human biomonitoring studies. The literature search led to 57 studies included in the review. Of these, 50 studies met the criteria to be used in the meta-analysis. Using standardized mean difference and 95% confidence interval (CI), the meta-analyses show increased levels of DNA strand breaks in subjects exposed to benzene (1.59, 95% CI: 0.94, 2.24), styrene (0.87, 95% CI: 0.23, 1.51), formaldehyde (0.39, 95% CI: -0.15, 0.92) and other organic solvents (2.14, 95% CI: 1.48, 2.81). Results originate mainly from studies on workers, with only a few studies on environmental benzene exposure. Subgroup analysis indicates that all studies combined from middle-income countries have a higher effect size (1.81, 95% CI: 1.26, 2.36, n = 28) than studies from high-income countries (0.87, 95% CI: 0.49, 1.24, n = 22). This difference between middle- and high-income countries may be due to differences in exposure levels or exposure assessment. However, this might not be the only reason, as sensitivity analysis indicates that effect sizes are at risk of comet assay measurement bias, as 78% (39 out of 50 studies) and 60% (30 studies) have not reported the use of assay controls and blinded analysis of samples, respectively. Relatively few studies have a high risk of bias due to an inadequate comet assay procedure description (14%, 7 studies) and exposure misclassification (16%, 8 studies). Limitations of the study were the differences in protocols, comet descriptors, exposure assessment and control for confounding factors among the studies. In conclusion, this systematic review and meta-analysis shows that exposure to VOCs - benzene, styrene, formaldehyde and others - is associated with increased levels of DNA strand breaks in human leukocytes.